Aldehydes are the most commonly used fixatives. They serve to stabilize the fine structural details of cells and tissues prior to examination by light or electron microscopy. Research workers, technicians, pathologists and others who regularly use aldehyde fixatives frequently do not appreciate the nature and properties of these compounds or the reasons for choosing to fix a specimen in formaldehyde, glutaraldehyde or a mixture of the two. Misconceptions are widespread also about formalin and paraformaldehyde, the commercial products from which formaldehyde-containing solutions are made.

For many years now, the combination of the modern S/TEM system (scanning/transmission electron microscope) with the X-ray energy dispersive spectrometer (XEDS) has resulted in Analytical Electron Microscopes (AEMs) able to deliver both high-resolution imaging and elemental composition maps in the same instrument. This ability to correlate local elemental composition with microstructure has greatly broadened the applications realm of the S/TEM instrument. The boundaries of performance for many of these applications are now determined by limits in XEDS system detection sensitivity. In this article, we describe an AEM with greatly enhanced detection sensitivity due to a number of innovations in the system architecture, including: a high-brightness Schottky FEG source, four detectors integrated deeply into the objective lens, windowless silicon drift detector technology with shutters, and high-speed electronics readout. This new system architecture provides many performance benefits, such as improved light element detection, better sample tilt response, faster mapping, and especially enhanced system detection sensitivity.

In order to get high resolution images from any scanning beam microscope one must be able to produce a sufficiently small probe, have a small interaction volume in the substrate and have an abundance of information-rich particles to collect to create the image. A typical scanning electron microscope is able to meet all of these requirements to some degree. However, a helium ion microscope based on a Gas Field Ion Source (GFIS) has significant advantages over the SEM in all three categories.

Atom probe tomography has primarily been used for atomic scale characterization of high electrical conductivity materials. A high electrical field applied to needle-shaped specimens evaporates surface atoms, and a time of flight measurement determines each atom's identity. A 2-dimensional detector determines each atom's original position on the specimen. When repeated successively over many surface monolayers, the original specimen can be reconstructed into a 3-dimensional representation. In order to have an accurate 3-D reconstruction of the original, the field required for atomic evaporation must be known a-priori. For many metallic materials, this evaporation field is well characterized, and 3-D reconstructions can be achieved with reasonable accuracy.

No longer are biologists content to peer through the oculars of a microscope. Eyes have been replaced by digital cameras. Instead of manual control of microscope stages, filters and light sources, modern microscopes have become fully robotic. Image acquisition and robotic movements require computer control. With such equipment it is possible to automatically record images at multiple wavelengths, carry out time-lapse recordings of living cells using very short exposure times and low light doses, and even to record images at multiple positions (e.g. from a multi-well plate) without operator intervention. Clearly, computer control of light microscope image acquisition is making many new experimental imaging strategies possible in the biological sciences.

X rays are universally valued for their ability to penetrate opaque objects. It is only within the past few decades that their short wavelengths have also been exploited to provide 3D imaging of the objects' interiors with resolution well beyond that of light microscopy (LM) in a wide variety of applications. This article explores X-ray imaging as a quantitative sub-micron nanoscale microscopy technique, and specifically its emergent role within the context of the central microscopy laboratory.

Spurr low viscosity embedding medium was introduced in 1969 and used vinyl cyclohexene dioxide (VCD or ERL 4206) as the low viscosity epoxy resin together with nonenyl succinic anhydride (NSA), the flexibilizer DER 736, and the accelerator dimethylaminoethanol (DMAE or S-1). This low viscosity formulation has been used extensively for embedding plant materials, microrganisms and other difficult specimens. Over the years numerous concerns about the toxicity and carcinogenicity of VCD have been raised. VCD (Fig. 1) was finally removed from the market in 2005 and replaced with ERL 4221 (Fig. 2), a cyclic epoxide with a higher molecular weight and higher viscosity. Vendors instructed that ERL 4221 be substituted for VCD at the same rates as used in the original Spurr formulation. This direct substitution resulted in a more viscous resin and blocks were extremely hard and brittle and lacked the sectioning qualities of the original formulation. Vendors then suggested modifications to the dehydration schedule and reductions in the amount of DMAE to improve the quality of the blocks.

One of the most important tasks of microscopy is to provide information about structures in their natural state. Since most life science microscopy procedures require fixation, dehydration, drying, and sectioning, diverse artefacts are unavoidable. It is also possible to dehydrate the water content of a specimen by freeze-drying. However, even relatively stable surface structures are changed during such treatments. Methods of liquid substitution and freezing-substitution show good results for biological specimens with a waxy solid coverage (Ensikat and Barthlott, 1993) and soft specimens in a mechanically deformed state (Gorb et al., 2000).

However, all these methods have certain restrictions for some types of specimens. For example, there are numerous biological surfaces covered with secretory fluids. Some specimens bear solid waxy coverings, which can be partly dissolved and washed out in organic solvents, such as ethanol, acetone, or propylenoxide. Often one would like to visualise dynamic processes (growth, deformation, or crystallisation) under environmental conditions, but at the high resolution in the SEM.

SEM observation of a specimen cross section can provide important information for research and development as well as failure analysis. In most cases, surface observation alone cannot provide information concerning the cross sectional structure of granular materials, layered materials, fibrous materials, and powders. Preparing highly-polished cross sections of these materials is both a science and an art.

Typically, a cross section is prepared using mechanical means like conventional mechanical polishing methods or a microtome. The sample is first embedded in a holder or device, and then polished to achieve a flat cross section. In some cases, a staining procedure is used to highlight a specific component of the sample. Such methods can be lengthy procedures that require a great deal of skill, and can introduce artifacts into soft materials, deform the material around voids, or compress layers of soft and hard materials in composite samples. Mechanical polishing can miss fine details such as the presence of hairline cracks, and present a challenge to water-soluble phases.

Microscopists demand better performance from their electron microscopes with every new instrument. With the advancement of new instrument technologies, better images, higher resolution, more precise analysis, and faster throughput are all benefits that are expected of expensive purchases. Still, in many cases, a well-known problem detrimentally affects the quality of results: specimen contamination.

Collecting good data is an important task, but handling the data correctly is important also. How to handle data largely depends on what the analyst is going to do with it. Electron backscatter diffraction (EBSD) is no exception.

Computed tomography (CT) has been commonly used in medicine for assessing the anatomy of humans in conventional computer axial tomography (CAT) scans. It is also a very common tool for assessing the architecture of trabecular bones for diagnosis of conditions such as osteoporosis. More recently, high-resolution CT (micro-CT) has found increasing use in materials science for the evaluation of the internal structure of a variety of advanced materials for industrial applications. Knowledge of the micro-architecture of these materials is extremely important to better understand their performance. Micro-CT is a non-destructive 3D characterization tool that uses X rays to determine the internal structure of objects through imaging of different densities within the scanned object. High-resolution laboratory-based micro-CT or nano-CT provides image resolution on the order of 300 nm. Such high resolution allows one to visualize the internal 3D structure of fine-scale features. The data from micro-CT results in a virtual rendering of the object under investigation, which allows one to travel through the volume in any direction and angle, revealing complex hidden structures within the object. Thus, micro-CT can be an important complementary technique for a microscopy laboratory.

The accuracy and precision of the quantitative measurements made with various types of scanning probe microscopes (SPMs) can be limited by instrumentation error. The piezoelectric scanners that are utilized in SPMs control either the motion of the cantilever probe with respect to a stationary sample or the motion of the sample with respect to a stationary probe. While these scanners offer many advantageous characteristics that are critical to the performance of SPMs, they also exhibit several behaviors, e.g., hysteresis and creep, that introduce uncertainties in measurements. Also, the nonlinearities associated with the photodiode used in the optical lever detection system can detract from the accuracy of measurements